1. Field of the Invention
This invention relates to snubbers and, more specifically, to a snubber for retarding movement of a door toward and away from an opening in a dipper.
2. Description of the Prior Art
When heavy objects are moved toward and away from each other, large inertia forces are created which must be counteracted to halt such movement. Such forces occur in large excavator dippers having heavy doors which open and close relative to discharge openings in the dippers. For example, a 15 cubic yard AMSCO.RTM. dipper has a door weighing 12,000 lbs. In operation, digging is begun with the door in a closed, substantially vertical position. When the bucket is full of mined rock, the dipper is rotated approximately 90.degree., elevated and moved to a discharge location, such as over a dump truck bed. The door is then opened, the mined rock is discharged, the bucket is again rotated 90.degree. and the door closes.
If a 12,000 lb. door is opened and closed without any snubbing device, the door will slam into the bucket on closing and possibly into the handle on opening with such force as to damage the door, its hinge, the dipper or the handle. It was early recognized that some device to arrest or snub the extreme movements of the door is necessary.
In the past, snubbers have been developed for connection between the door and the dipper. These have taken the form of spring, friction or hydraulic snubbers. None of these has been found suitable in commercial use. Springs generally do not create sufficient force and can be fouled by rocks wedged between the coils. Hydraulic devices are extremely complicated and subject to such high pressures that they leak. Additionally, they are easily damaged by falling rock. Friction devices are most common in commercial usage, but are plagued by the necessity for constant adjustment due to rapid wear and cause much down-time because of a short useful life.
There exists a definite need for a device to snub the relative movement of heavy objects toward and away from each other, such as dipper doors, that has extended life, is relatively impervious to rock damage, is easy to install and provides sufficient snubbing forces.